1. Field of the Invention
The present invention relates to a method for the measurement of an aberration of an optical projection system and, more particularly, to an aberration measurement method for measuring an aberration of an optical projection system of a projection exposure apparatus to be utilized in particular for the manufacture of devices such as semiconductor elements and liquid crystal display elements.
2. Description of the Related Art
As the extent of integration of circuit patterns for semiconductor elements and so on develops greater and greater, the structure of such patterns is being made finer and finer from year to year. Accordingly, an exposure apparatus of a projection type for resolving a pattern should be developed so as to catch up with developments of making the pattern finer and making the exposing wavelength from 365 nm to 248 nm. At the same time, various aberrations of an optical projection system of the exposure apparatus should be made considerably less because of such developments.
Hitherto, the measurement of an asymmetrical aberration of a projection lens, which includes a comatic aberration of a projection lens and a comatic aberration caused by eccentricity of a mechanical center of the projection lens from the light axis, has been made by locating a light shade pattern at a light transmission section on a reticle in such a state where the projection lens is disposed in the projection exposure apparatus, transcribing the light shade pattern onto a substrate coated with a photoresist and then inspecting an asymmetrical amount of the photoresist image of the pattern transcribed with an electronic microscope or other means.
In order to inspect such an asymmetrical amount of the photoresist image, however, a measuring device having a resolving power of 0.005 .mu.m is required and only a scanning type electronic microscope (SEM) of the latest type can meet such requirements. The SEM may cause problems, however, in that the resolving power thereof may vary with alignment of the optical axis of an optical electronic system or pressure of inner gases, i.e., a degree of vacuum, or other conditions and, therefore, that the resolving power of the SEM may vary with the ability of researchers who handle it, the state of the apparatus, or the like. Further, the difference of the resolving power can exert a big influence upon an amount of an aberration to be measured.